A scoping study on the prevalence of Escherichia coli and Enterococcus species in harvested rainwater stored in tanks

Abstract

Rainwater harvesting (RWH) is a relatively inexpensive technology that has the potential to provide safe water in communities where conventional technologies are difficult to implement. In this study, the microbiological quality of rainwater harvested from rooftops and ground-surface runoff was evaluated based on the concentrations of Escherichia coli, total coliforms and enterococci. Samples were collected from 15 roof-harvested rainwater (RHRW) tanks, 4 ground-surface runoff rainwater harvesting (GRWH) tanks, 3 rivers and 1 spring water source in the Eastern Cape Province of South Africa, and 14 RHRW tanks in Gauteng Province. In the Eastern Cape Province E. coli and enterococci were detected in 7 and 4 of the 15 RHRW tanks, respectively. Enterococci were detected only from one river whereas E. coli was detected in all three rivers; in spring water neither enterococci nor E. coli were detected. Samples from GRWH tanks were positive for E. coli and enterococci in 2 and 3 of the 4 tanks, respectively. In Gauteng Province, E. coli, coliforms and enterococci were detected from 6, 6 and 9 of the 14 rainwater tanks, respectively. On average, E. coli and enterococci were detected in 44.8% of the RHRW tanks, although enterococci concentrations were several times higher than those for E. coli. We further evaluated the significance of urban pigeons as the likely sources of contamination by isolating 156 enterococci from 30 pigeon faecal samples and 208 enterococci from RHRW samples collected from Gauteng Province. Matrix-assisted laser desorption ionisation identification of the various enterococci revealed 4 species – E. faecalis (20.5%), E. mundtii (20.51%), E. faecium (23.1%) and E. casseliflavus (17.3%) – to be dominant in faecal samples, whereas E. casseliflavus (34.6%) and E. mundtii (33.2%) were dominant in RHRW.

Keywords: rainwater harvesting, contamination, indicator bacteria, health risks